Symbiont infection affects aphid defensive behaviours

International audienceAphids harbour both an obligate bacterial symbiont, Buchnera aphidicola, and a wide range of facultative ones. acultative symbionts can modify morphological, developmental and physiological host traits that favour their spread within aphid populations. We experimentally investigated the idea that symbionts may also modify aphid behavioural traits to enhance their transmission. Aphids exhibit many behavioural defences against enemies. Despite their benefits, these behaviours have some associated costs leading to reduction in aphid reproduction. Some aphid individuals harbour a facultative symbiont Hamiltonella defensa that provides protection against parasitoids. By analyzing aphid behaviours in the presence of parasitoids, we showed that aphids infected with H. defense exhibited reduced aggressiveness and escape reactions compared with uninfected aphids. The aphid and the symbiont have both benefited from these behavioural changes: both partners reduced the fitness decrements associated with the behavioural defences. Such symbiontinduced changes of behavioural defences may have consequences for oevolutionary processes between host organisms and their enemies.